Catch and report unhandled rejections

Promise rejection events are not widely supported yet, but we can rely
on them in Chrome. This closes a blind spot our reporting system has
when it comes to uncaught exceptions in asynchronous operations.

Change-Id: I3ee2def42ee3dfb9162b5d6386bf3cf9f5e00cf9

polygerrit-ui/app/elements/core/gr-reporting/gr-reporting.js

@@ -64,6 +64,13 @@
   const catchErrors = function(opt_context) {
     const context = opt_context || window;
     context.onerror = onError.bind(null, context.onerror);
+    context.addEventListener('unhandledrejection', e => {
+      const msg = e.reason.message;
+      const payload = {
+        error: e.reason,
+      };
+      GrReporting.prototype.reporter(ERROR.TYPE, ERROR.CATEGORY, msg, payload);
+    });
   };
   catchErrors();
 

polygerrit-ui/app/elements/core/gr-reporting/gr-reporting_test.html

@@ -183,7 +183,12 @@ limitations under the License.
 
       setup(() => {
         reporter = sandbox.stub(GrReporting.prototype, 'reporter');
-        fakeWindow = {};
+        fakeWindow = {
+          handlers: {},
+          addEventListener(type, handler) {
+            this.handlers[type] = handler;
+          },
+        };
         sandbox.stub(console, 'error');
         window.GrReporting._catchErrors(fakeWindow);
       });
@@ -204,6 +209,15 @@ limitations under the License.
       test('prevent default event handler', () => {
         assert.isTrue(emulateThrow());
       });
+
+      test('unhandled rejection', () => {
+        fakeWindow.handlers['unhandledrejection']({
+          reason: {
+            message: 'bar',
+          },
+        });
+        assert.isTrue(reporter.calledWith('error', 'exception', 'bar'));
+      });
     });
   });
 </script>